The Collaborative International Dictionary of English v.0.48:

Achaean \A*ch[ae]"an\, Achaian \A*cha"ian\a. [L. Achaeus,
   Achaius; Gr. ?.]
   Of or pertaining to Achaia in Greece; also, Grecian. -- n. A
   native of Achaia; a Greek.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Achaean
    adj 1: of or relating to Achaea or its ancient Greek people
    n 1: a member of one of four linguistic divisions of the
         prehistoric Greeks [syn: Achaean, Achaian]
    2: the ancient Greek inhabitants of Achaea [syn: Achaean,
       Arcado-Cyprians]